When we discuss whether an animal is mu’ad (has a violent history) or tam (has no history of violence) we usually are talking about domesticated animals. The Mishna (15b) teaches that wild animals, e.g. lions and tigers and bears, are intrinsically mu’adim and their owners will always be responsible for them.
With regard to this halakha, our Gemara introduces Shmuel’s opinion that even wild animals will only be considered mu’adim if they behave in a manner that is normal for them. Thus, if a lion in is the public domain and kills in its normal manner, the owner is responsible, but if the lion kills in an abnormal way, the owner will not be fully responsible.
The Maharshal in his Yam Shel Shlomo objects to Shmuel’s teaching – is it possible that the halakha would permit someone to place a wild animal in the public domain and would not even hold him responsible!? How could someone be permitted to endanger the community in that way? The Maharshal suggests that although this is not the ideal, nevertheless once we recognize the overarching rule that the owner of an animal that behaves abnormally in the public domain is not responsible, it will be applied in all cases – even this one – since such a case is most unusual, and therefore there is no need to develop separate legislation for it. The Nahalat David rules that Shmuel’s ruling notwithstanding, no one would be permitted to bring a wild animal into the public domain. This can be proven by the fact that the sages even obligated the owner of a kelev ra – a bad tempered dog – to remove it as a danger, certainly a case like this one.
As far as the halakha is concerned, the Rambam rejects Shmuel’s distinction and rules that the owner of any wild animal that attacks another animal in the public domain will be held responsible; any method of attack is considered “normal” for a wild animal (see Hilkhot Nizkei Mamon 3:7). The R”i and others accept Shmuel’s ruling and argue that in a case where a wild animal injures another animal in a manner that is not normal for it, the owner will only be obligated to pay half damages, since we treat the animal as a tam (an animal with no previous history of violence) since it behaved in an unexpected manner.